Rattus leucopus species group. Described as an unusual and distinctive member of Rattus, but later provisionally associated with a "niobe group" (Tate, 1951), a relationship supported by multivariate analyses of morphometric variables (Taylor et al., 1982). Most specimens are from tussock grassland and tundra-like habitat (mainly rock or gravel interspersed with mats of herbs and grass tufts), regions that are cold and wet throughout the year (Flannery, 1995a; Taylor et al., 1982). Taylor et al. (1982) included omichlodes, but Flannery (1995a) correctly removed it from synonymy (see that account).